• Title/Summary/Keyword: 콘크리트 응력 수준 평가

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Permeability Evaluation in Cold Joint Concrete with Mineral Admixture under Compressive and Tensile Loading (혼화재료를 고려한 압축 및 인장상태에서 콜드조인트 콘크리트의 투수성 평가)

  • Choi, Se-Jin;Kim, Seong-Jun;Mun, Jin-Man;Kwon, Seung-Jun
    • The Journal of the Korea Contents Association
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    • v.15 no.9
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    • pp.576-587
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    • 2015
  • This paper presents a quantitative evaluation of water permeability in concrete with cold joint considering mineral admixture and loading conditions. Concrete samples with OPC (Ordinary Portland Cement) and GGBFS(Ground Granulated Blast Furnace Slag) are prepared considering 0.6 of W/C ratio and 40% of replacement. 30% and 60% loading levels for compression and 60% loading level for tension are induced to concrete samples. In compression conditions, the permeability in control case shows $2.41{\times}10^{-11}m/s$ in OPC concrete, and it changes to $2.07{\times}10^{-11}m/s$ (30% of peak) and $2.36{\times}10^{-11}m/s$ (60% of peak). The results in GGBFS concrete shows the same trend, which yields $2.17{\times}10^{-11}m/s$ (control), $1.65{\times}10^{-11}m/s$ (30% of peak), and $1.96{\times}10^{-11}m/s$ (60% of peak), respectively. In tensile conditions, the permeability increases from $2.37{\times}10^{-11}m/s$ (control) to $2.67{\times}10^{-11}m/s$ (60% of peak) while that in GGBFS concrete increases from $2.17{\times}10^{-11}m/s$ (control) to $2.24{\times}10^{-11}m/s$ (60% of peak). Permeability coefficients decreases in 30% of compressive level but increases in 60% level, while results in tensile level increases rapidly. This shows pore structure in concrete is condensed and with loading and permeability increases due to micro-cracking. Permeability evaluation considering the effects of loading conditions, cold joint, and GGBFS is verified to be important since water permeability greatly changes due to their effects.

The Fatigue Crack Growth Behavior of Concrete (콘크리트의 피로균열 성장거동에 관한 연구)

  • 김진근;김윤용
    • Magazine of the Korea Concrete Institute
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    • v.9 no.3
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    • pp.127-135
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    • 1997
  • In this study, the wedge splitting tcst (WST) was carried out for the fatigue wack growth behavior of concrete. Selected test variables were concrete compressive strength of 28, 60 and 118 MI%, and stress ratio with 2 levels (6. 13%). In oder to make the designed stress ratio, the maximum and thr minimum fatigue loading level were 75-85% and 5- 10% of ultimate static load, respectively. Fatigue testing was preceded by crack mout.h opening displacement (CMOI)) compliance calibration tcst, and then the fatigue crack growth was computed by crack lcngth vs. (lMOI) compliance relations acquisited by the CMOD compliance calibration technique. To evaluate thc validity of CMOD compliancc calibration techniquc, the crack length p~mlicted by this method was cornpard with the crack length by linear elastic fracture mechanics(LEFIbl) and dyeing test. On the basis of the experimental results, a LRFhl-based c.mpirica1 model for f'at,igue crack growth rate(da/dN-AKI relationships) was presented. The fat,igut. crack growth ratc increased with the strength of concwtc. It appcars that t.he da/tiN-AKI relationships was influenced by stress ratio, however, the effect is diminished with an increase of strength. The comparisons between CblOl) compliance calibration technique anti the other. methods gave the validity of' ('MOD compliance calibration technique for the LZXT.

Modeling on Ultrasonic Velocity in Concrete Considering Micro Pore Structure and Loading Conditions (공극구조 및 하중조건에 따른 콘크리트의 초음파 속도 모델링)

  • Kim, Yun Yong;Oh, Kwang-Chin;Park, Ki-Tae;Kwon, Seung-Jun
    • The Journal of the Korea Contents Association
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    • v.15 no.3
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    • pp.415-426
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    • 2015
  • For a long time, evaluation of soundness and strength in concrete has been performed through ultrasonic velocity(UV), which is essential work in field assessment. Porosity in concrete is a major parameter indicating durability and strength, and UV passing concrete depends on porosity variation. In this paper, a modeling on UV through concrete is carried out considering porosity and the results are verified with those from test. Additionally UV in concrete under compression/tension loading condition is measured and UV modeling with loading condition is performed. Up to 50% of loading ratio, UV slightly increases and greatly drops at peak load in compression region, however it fluctuates in tensile region due to micro cracking in matrix. The proposed model shows a reasonable agreement with test results in control and compression region, and needs modification for tensile region considering micro cracks and local aggregate interlocking.

A Study on Effect of Anchor Plate on Concrete Breakout Capacity and Elasticity-Based Analysis Model of Anchor Plate (앵커플레이트가 콘크리트 파괴 강도에 미치는 영향 및 탄성기반 해석 모델에 대한 연구)

  • Shin, Ji-Uk;You, Young-Chan;Choi, Ki-Seon;Kim, Ho-Ryong;Kim, Jun-Hee
    • Journal of the Korea Concrete Institute
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    • v.25 no.4
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    • pp.381-388
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    • 2013
  • This study presents that effect of anchor plate on concrete breakout strength was evaluated. The addition of the anchor plate is to improve the concrete breakout capacity for a single anchor system in a thin-walled concrete panel (Insulated concrete sandwich wall panel). In this study, an elasticity-based simplified model was developed and used to predict effect on the anchor plate. Flexural stresses of the plate with respect to the concrete breakout strength obtained from CCD (Capacity Concrete Design) approach were compared with the test results. Through the test results, while the concrete breakout strength was improved due to increment of the width and thickness of the anchor plate, improvement of the strength was steadily declined. In addition, the It was observed that the analytical and experimental flexure of the anchor plate was comparatively in good agreement using the simplified elastic analysis model.

Effect of Partial Prestressing Ratio and Effective Prestress on the Flexural Behavior of Prestressed Lightweight Concrete Beams (프리스트레스트 경량 콘크리트 보의 휨 거동에 대한 부분 프리스트레싱비와 유효 프리스트레스의 영향)

  • Yang, Keun-Hyeok;Moon, Ju-Hyun;Byun, Hang-Yong
    • Journal of the Korea Concrete Institute
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    • v.23 no.1
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    • pp.39-48
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    • 2011
  • The present investigation evaluates the flexural behavior of pre-tensioned lightweight concrete beams under two-point symmetrical concentrated loads according to the variation of the partial prestressing ratio and the effective prestress of prestressing strands. The designed compressive strength of the lightweight concrete with a dry density of 1,770 $kg/m^3$ was 35 MPa. The deformed bar with a yield strength of 383 MPa and three-wire mono-strands with tensile strength of 2,040 MPa were used for longitudinal tensile reinforcement and prestressing steel reinforcement, respectively. According to the test results, the flexural capacity of pre-tensioned lightweight concrete beams increased with the increase of the partial prestressing ratio and was marginally influenced by the effective prestress of strands. With the same reinforcing index, the normalized flexural capacity of pre-tensioned lightweight concrete beams was similar to that of pre-tensioned normal-weight concrete beams tested by Harajli and Naaman and Bennett. On the other hand, the displacement ductility ratio of pre-tensioned lightweight concrete beams increased with the decrease of the partial prestressing ratio and with the increase of the effective prestress of strands. The load-displacement relationship of pre-tensioned lightweight concrete beam specimens can be suitably predicted by the developed non-linear two-dimensional analysis procedure. In addition, the flexural cracking moment and flexural capacity of pre-tensioned lightweight concrete beams can be conservatively evaluated using the elasticity theorem and the approach specified in ACI 318-08, respectively.

Seismic Performance of Reinforced Concrete Shear Wall Buildings with Piloti (필로티를 갖는 철근콘크리트 전단벽식 건물의 내진성능)

  • Kwon Young-Wung;Kim Min-Su
    • Journal of the Korea Concrete Institute
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    • v.17 no.4 s.88
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    • pp.587-594
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    • 2005
  • The purpose of seismic design is to ensure the serviceability of buildings against earthquake, which might be occurred during the service life of buildings, and to minimize the loss of life by preventing their failure under strong earthquake. The lack resistance of walls resulting from a tendency toward high-rise apartment buildings with shear walls and use of piloti would lead to a concentration of inelastic behaviors in their weak story. In this study, the seismic performance of reinforced concrete shear wall buildings haying piloti was analyzed by using the evaluation techniques which was proposed by FEMA 273 and ATC-40. The results from comparison with these two techniques are summarized as follows.; The results of elastic analysis method for seismic performance evaluation show that the effect of piloti and building height decrease performance index. In case of shear wall building, the state of insufficient shear stress governs their overall performance and it becomes evident in the case of the buildings with more than 25 stories. For the buildings of piloti, the change of mass, weak story, as well as insufficient shear stress, decrease the performance index rapidly compared with the performance index of the buildings without piloti. The results, obtained from the nonlinear static analysis using capacity spectrum method, indicate that the performance Point increases for the structure having Piloti and high story. Also, deformation limits of buildings satisfy the allowable criteria at the life safety level, but the immediate occupancy level is exceeded in buildings which have more than 25 stories.

Prediction of the Rheological Properties of Cement Mortar Applying Multiscale Techniques (멀티스케일 기법을 적용한 시멘트 모르타르의 유변특성 예측)

  • Eun-Seok Choi;Jun-Woo Lee;Su-Tae Kang
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.28 no.2
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    • pp.69-76
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    • 2024
  • The rheological properties of fresh concrete significantly influence its manufacturing and performance. However, the diversification of newly developed mixtures and manufacturing techniques has made it challenging to accurately predict these properties using traditional empirical methods. This study introduces a multiscale rheological property prediction model designed to quantitatively anticipate the rheological characteristics from nano-scale interparticle interactions, such as those among cement particles, to micro-scale behaviors, such as those involving fine aggregates. The Yield Stress Model (YODEL), the Chateau-Ovarlez-Trung equation, and the Krieger-Dougherty equation were utilized to predict the yield stress for cement paste and mortar, as well as the plastic viscosity. Initially, predictions were made for the paste scale, using the water-cement ratio (W/C) of the cement paste. These predictions then served as a basis for further forecasting of the rheological properties at the mortar scale, incorporating the same W/C and adding the cement-sand volume ratio (C/S). Lastly, the practicality of the predictive model was assessed by comparing the forecasted outcomes to experimental results obtained from rotational rheometer.

Experiment of Flexural Behavior of Reinforced Concrete Beams with High Volume Fly Ash (하이 볼륨 플라이애쉬 철근콘크리트 보의 휨거동 실험)

  • Yoo, Sung-Won;Lee, Hyung-Jib
    • Journal of the Korea Concrete Institute
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    • v.26 no.3
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    • pp.323-329
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    • 2014
  • It is known that the best way to recycle fly ash is to use in concrete. It is impossible to bury in the ground this fly ash recently, so it is trying to use high volume fly ash concrete. Nevertheless, recent main research topics are focused in the part of material only, however, it is necessary to perform the researches about elasticity modulus, stress-strain relationship and structural behavior. Therefore, in this paper, 18 test members were manufactured with 3 test variables, namely fly ash replacement ratio 0, 35, 50%, concrete compressive strength 20, 40, 60 MPa and 2 tensile steel ratio. 18 test members were tested for flexural behavior. From the test results, there were no differences between 35, 50% high volume fly ash cement concrete and ordinary concrete without fly ash(FA=0%).

Experimental Study and Evaluation of Tension Stiffening Model in High Strength Concrete Beams (고강도 콘크리트 보에서 Tension Stiffening 모델을 이용한 실험적 연구 및 평가)

  • Shin, Dae Hwan;Jo, Eunsun;Kim, Min Sook;Kim, Heechuel;Lee, Young Hak
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.27 no.1
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    • pp.45-53
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    • 2014
  • In strength limit states design, it is assumed that after cracking, reinforcement carries all tension in the tension zone of reinforced concrete members. However, it can be seen the concrete between cracks will contribute to carrying a part of the tension stress in actual concrete members particularly at service load levels, this effect is referred as tension stiffening effect. In this study, tension stiffening models and high strength concrete beam flexural test results were verified through comparison. The relationship between moment-curvature and load-deflection was evaluated by result of tension stiffening model and test result values. The analysis results showed that ACI 318 and Owen & Damjanic generally shows good agreement.

Evaluation of Proper Level of the Longitudinal Prestress for the Precast Deck of Railway Bridges Considering the Temperature Change (철도교용 프리케스트 바닥판의 온도변화를 고려한 적정한 종방향 프리스트레스 수준의 산정)

  • Jeon, Se Jin;Kim, Young Jin;Kim, Seong Woon;Kim, Cheol Young
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.3D
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    • pp.499-509
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    • 2006
  • Precast concrete deck has many advantages comparing with the in-situ concrete deck, and has been successfully applied to replacement of the deteriorated decks and to the newly constructed highway bridges in domestic region. In order to apply the precast decks into the railway bridges, however, differences of the load characteristics between the highway and the railway should be properly taken into account including the train load, longitudinal force of the continuous welded rail, acceleration or braking force, temperature change and shrinkage. Proper level of the longitudinal prestress of the tendons that can ensure integrity of the transverse joints in the deck system is of a primary importance. To this aim, the longitudinal tensile stresses induced by the design loads are derived using three-dimensional finite element analyses for the frequently adopted PSC composite girder railway bridge. The effect of the temperature change is also investigated considering the design codes and theoretical equations in an in-depth manner. The estimated proper prestress level to counteract those tensile stresses is above 2.4 MPa, which is similar to the case of the highway bridges.